1. Field of the Invention
The present invention relates to a dynamic host configuration protocol (DHCP) server, which dynamically allocates IP addresses to client devices, to which host names are given, connected to a Transmission Control Protocol/Internet Protocol (TCP/IP) network, and an IP address allocating method using the same.
2. Description of the Related Art
Variety of recent network systems require to make settings and management in the TCP/IP network simple and further require to effectively allocate short IP address resources.
Therefore, the Internet Engineering Task Force (IETF) has standardized the Dynamic Host Configuration Protocol (DHCP).
When plural hosts, i.e., clients for a DHCP server, concurrently access to one network, for example, messages broadcasted between the DHCP clients and the DHCP server are increased before allocating IP addresses. That also causes increasing of traffic loads, which are required to be avoided.
FIGS. 14 to 17 show operations between the DHCP clients and the DHCP servers when plural DHCP servers are provided on one TCP/IP network till a client xe2x80x9caxe2x80x9d obtains an IP address.
Before the IP address is allocated by the DHCP function, the DHCP client xe2x80x9caxe2x80x9d can not unicast, i.e., send a request signal for a specified server because there is no IP address. Therefore, it becomes possible to facilitate communications by broadcasting, i.e., sending arequest signal for all servers.
In FIGS. 14 to 17, xe2x80x9caxe2x80x9d to xe2x80x9cexe2x80x9d respectively denote standard DHCP clients, and xe2x80x9cAxe2x80x9d to xe2x80x9cDxe2x80x9d respectively denote standard DHCP servers.
At first, the client xe2x80x9caxe2x80x9d broadcasts a DHCPDISCOVER message including lease information that the client xe2x80x9caxe2x80x9d wants to obtain, i.e., IP address, sub-net mask and so on, to the DHCP servers xe2x80x9cAxe2x80x9d to xe2x80x9cDxe2x80x9d with the own media access control (MAC) address (refer to FIG. 14). A sub-net mask is an address obtained by that a host address is divided into plural small networks or sub-networks.
Secondly, the DHCP servers xe2x80x9cAxe2x80x9d to xe2x80x9cDxe2x80x9d, which receive the DHCPDISCOVER message, respectively broadcast the requested lease information with a DHCPOFFER message.
The DHCPOFFER message includes a MAC address of the client xe2x80x9caxe2x80x9d that has requested the lease information. Therefore, the client xe2x80x9caxe2x80x9d acknowledges the massage is addressed to himself after then (refer to FIG. 15).
Next, the client xe2x80x9caxe2x80x9d collects DHCPOFFER messages during a certain interval, selects one from the plural messages, and broadcasts the server ID or the required information value, i.e., which IP address leased from a DHCP server is used, as a DHCPREQUEST message (refer to FIG. 16).
Then, the DHCP server A decides the IP address when the leased IP address is idle, and unicasts a DHCPACK message, i.e., an acknowledging message, to the client xe2x80x9caxe2x80x9d (refer to FIG. 17).
However, as all of the hosts A to D connected to one network require the above-described operations, the number of calls of the broadcasted messages increases. That causes an increase of traffic load according to the following conditions;
where there are many hosts connected to one network, and
plural DHCP servers; and
timings when clients allocate IP addresses are overlapped.
This causes a problem such that the broadcasted messages are increased before allocating the IP addresses, if the number of hosts and DHCP servers, each of which becomes a DHCP client connected to the TCP/IP network, becomes large.
Accordingly, it is an object of the present invention to provide a DHCP server system, in which only a specific DHCP server sends a DHCPOFFER message for a DHCPDISCOVER message sent from a DHCP client.
It is another object of the present invention to provide an IP address allocating method using the above-described DHCP server system.
The above-described objects can be attained by a DHCP server according to the present invention, by using an IP address allocating method, by which a server allocates an IP address to each client who is one of plural clients connected to a transmission control protocol/Internet protocol (TCP/IP) network on a LAN, by using a dynamic host configuration protocol (DHCP).
The client broadcasts an IP address lease information, which a client wants to obtain from the client.
The server checks whether or not the host name of the client who sent the IP address lease information is coincident with one of host names registered in a host management database.
Then, the server broadcasts a temporally allocated IP address when both of the host names are coincident, the client sending the IP address lease information unicasts an IP address request to the server, the server receiving the IP address request unicasted from the client unicasts an IP address attaching confirmation to the client.
The host management database registers host names of the plural clients, and the sent host name is checked by comparing the host name sent from the client with the registered host names to confirm whether or not any one of the registered host names is perfectly coincident to the host name sent by the client.
The host management database stores a part of each of the plural host names of the clients as registered data, and checks whether or not a part of the host name sent by the client is coincident with any one of the stored parts of the plural host names.